The long-term goal of this study is to develop valid and reliable tests for screening people for vestibular (inner ear) disorders, so that those tests can be used in studies of the American population to determine the frequency of vestibular disorders in the general population. We also expect that these tests will be useful in nursing homes and other facilities with limited resources for testing, and at landing sites for astronauts after returning from long duration space flight. In Specific Aim 1 we will complete test development, including developing age-appropriate norms for a test of standing balance, and we will determine which tests best distinguish healthy controls from people with known vestibular disorders. In Specific Aim 2 we will test the test battery, to determine how well the tet battery predicts who in the general population has a vestibular impairment. Participants will be given the test battery and then will be tested in the diagnostic laboratory with the standard battery of objective diagnostic tests. Using the new test battery in Specific Aim 2A we will screen people recruited from clinics at Baylor College of Medicine. The screening environment at Baylor College of Medicine will be well-controlled so that we will be able to work out any technical bugs in the system. Using the new screening battery we will also test people at a distant site, the Washington, DC site of the Women's Interagency HIV Study (WIHS). The WIHS includes participants who have HIV or AIDS and participants who are age-matched healthy controls. At this site we will have less control over the screening environment but will work with an excellent, well-established epidemiologic team to determine not only how well the tests predict results from the diagnostic laboratory but also how easy the battery is for staff to administer. Additional benefits of testing the WIHS cohort, men recruited from the Infectious Disease clinic at Georgetown University Medical Center, and men from the community who do not have HIV/AIDS, will be the ability to learn more about the effects of HIV/AIDS on vestibular disorders in middle-aged and early-elderly people who also represent underserved populations that are rarely, if ever, invited to participate in research on vestibular and balance disorders, ie., homosexual/ bisexual men and low-income, minority women in the WIHS. Because these tests may also be used in community health centers where homosexual/ bisexual men and low income, minority women with HIV/AIDS often receive health care developing these tests may improve the quality of care available to those subpopulations.